Author + information
- Anthony C. Camuglia, MBBS (Hons),
- Jaffer Syed, MD, MEd,
- Pallav Garg, MBBS, MSc,
- Bob Kiaii, MD,
- Michael W. Chu, MD, MEd,
- Philip M. Jones, MD, MSc,
- Daniel Bainbridge, MD and
- Patrick J. Teefy, MD∗ ()
- ↵∗Department of Interventional Cardiology, London Health Sciences Centre, 339 Windermere Road, London, Ontario, N6A 5A5, Canada
To the Editor:
Valvular aortic stenosis (AS) leads to several pathophysiological changes. These result in cardiac dysfunction, with attendant symptoms and, if not managed appropriately, poor clinical outcomes. Impairment of coronary flow dynamics, as measured by coronary flow reserve (CFR), has been identified as a likely major contributor toward the adverse outcomes that occur in patients with severe AS (1,2). We therefore sought to assess the effect of transcatheter aortic valve implantation (TAVI) on coronary flow dynamics as assessed by invasive CFR measurement in patients undergoing TAVI for severe AS.
The study design consisted of enrollment of consecutive patients undergoing transfemoral TAVI for severe AS at University Hospital, London Health Sciences Centre, London, Ontario, Canada. Inclusion criteria included documented symptomatic severe AS (aortic valve mean gradient on transthoracic echocardiography of >40 mm Hg, peak aortic valve velocity of >4 m/s, and aortic valve area of <1.0 cm2), high risk to undergo conventional aortic valve replacement, and planned for transfemoral TAVI procedure in a hybrid operating room equipped with angiographic equipment. Patients undergoing TAVI via the transaortic or transapical approach were excluded. The study protocol was reviewed and approved by the ethics board of the University of Western Ontario, and patients gave written informed consent.
CFR was assessed at the time of the TAVI procedure. In brief, the bypass graft or vessel of interest (native vessel was used when possible) was engaged with a 6-F guiding catheter under fluoroscopic guidance. The coronary arterial circulation supplying the left ventricle was assessed for either a native vessel or a saphenous vein graft free of significant angiographic stenosis (>30%) visualized in the graft or in the target vessel beyond the distal graft anastomosis. Following this a 0.014-inch Doppler-tipped coronary flow wire (FloWire, Volcano Corporation, San Diego, California) was then inserted into the vessel of interest, with hemodynamic data recorded using the Volcano s5 system. Intracoronary glyceryl trinitrate 100 μg was then administered prior to the administration of intracoronary adenosine. Adenosine was administered in 3 increments using a concentration of 6 μg/ml to a dose of 120 μg to induce maximal hyperemia. CFR was calculated as the ratio of maximal hyperemic average peak velocity (APV) to pre-hyperemia basal levels (APVpost/APVpre). The procedure was then repeated immediately following TAVI, while the patient was still on the procedure table, and again at a separate follow-up study 12 months from the date of TAVI.
The target study size was 10 patients. Paired samples were compared using paired Student t test or Wilcoxon matched pairs rank-sum test (as appropriate based on whether the data was judged as being parametrically distributed using the Shapiro-Wilk test). Repeated-measures analysis of variance was used for multiple-group comparisons. Calculations and analysis were performed using SAS JMP version 10.0.2.
Ten patients were enrolled in the study and underwent the initial invasive assessment. However, 1 patient died during the follow-up period and another patient declined repeat invasive assessment due to advanced age; therefore, data were available for 8 patients. All patients had a mean atrioventricular gradient >40 mm Hg and received CoreValve (Medtronic, Inc., Minneapolis, Minnesota) implantation by the transfemoral approach. Mean aortic valve pressure gradients as assessed by transthoracic echocardiography decreased from 56.3 mm Hg (95% CI: 48.7 to 63.9 mm Hg) to 11.8 mm Hg (95% CI: 8.6 to 14.9 mm Hg; p < 0.01) at 12-month follow-up.
Using a cutoff value for the CFR ratio of 2.5 (the expected normal), all patients had impaired CFR prior to TAVI (mean CFR 1.53; 95% CI: 1.27 to 1.8). At follow-up invasive assessment at a mean of 376 days, there was a significant increase in CFR among the 8 patients (mean absolute increase in CFR at follow-up vs. pre-TAVI of 0.65; 95 CI: 0.36 to 0.93; p < 0.01) with a mean CFR of 2.18 (95% CI: 1.88 to 2.47). Although there was a significant change from baseline pre-TAVI measurements to follow-up, there was no significant improvement in CFR immediately post TAVI (mean change in CFR immediately post-TAVI vs. pre-TAVI of 0.045; 95% CI: −0.4 to 0.49; p = 0.41). These data are also demonstrated in Figures 1A and 1B, and Figure 1C demonstrates the raw APV data pre- and post-hyperemia induction at each time point. There were no adverse events as a result of the invasive CFR evaluation. The vessel interrogated with the saphenous vein graft to the left circumflex artery in 6 patients (native vessels too diseased upstream) and the native left circumflex artery in 2 patients. Two cardiologists trained in CFR assessment reviewed the raw traces and made CFR measurements with the results compared for interobserver variability. There were no statistically significant differences between the 2 sets of measurements, and both sets of measurements independently (and when averaged) demonstrated the same positive primary outcome.
Our data showed that treatment of AS by relieving the mechanical obstruction with TAVI led to a significant improvement in CFR at medium-term follow-up. This is the first study to demonstrate this serially using invasive assessments, although it has been assessed indirectly using noninvasive techniques in 2 noninvasive studies on patients undergoing conventional aortic valve replacement (3,4).
Limitations of this study include the small sample size. However, the difficulty of performing the current study (serial invasive measurements sometimes requiring guide catheter cannulation between CoreValve struts) may explain why it has not been done previously. However, the magnitude of the change in the principal variable is consistent with that in other previous noninvasive studies.
In conclusion, we report that the treatment of severe AS with TAVI led to a significant improvement in coronary flow dynamics at 12-month follow-up as measured by CFR. This potentially represents one of the key physiological pathways that is responsible for symptomatic and prognostic improvement of patients with AS who are treated with TAVI.
Please note: Drs. Kiaii and Chu have received consulting fees from Medtronic. Dr. Teefy received consulting fees and honoraria for lectures and served on advisory boards for Medtronic. All other authors have reported that they have no relationships relevant to the contents of this paper to disclose.
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